Photovoltaic (PV) devices or solar cells are devices which convert sunlight into direct current (DC) electrical power. Typical thin film PV devices, or thin film solar cells, have one or more p-i-n junctions. Each p-i-n junction comprises a p-type layer, an intrinsic type layer, and an n-type layer. When the p-i-n junction of the solar cell is exposed to sunlight (consisting of energy from photons), the sunlight is converted to electricity through the PV effect. Solar cells may be tiled into larger solar arrays. The solar arrays are created by connecting a number of solar cells and joining them into panels with specific frames and connectors.
Typically, a thin film solar cell includes active regions, or photoelectric conversion units, and a transparent conductive oxide (TCO) film disposed as a front electrode and/or as a back electrode. The photoelectric conversion unit includes a p-type silicon layer, an n-type silicon layer, and an intrinsic type (i-type) silicon layer sandwiched between the p-type and n-type silicon layers. Several types of silicon films including microcrystalline silicon film (μc-Si), amorphous silicon film (a-Si), polycrystalline silicon film (poly-Si), and the like may be utilized to form the p-type, n-type, and/or i-type layers of the photoelectric conversion unit. The backside electrode may contain one or more conductive layers.
With traditional energy source prices on the rise, there is a need for a low cost way of producing electricity using a low cost solar cell device. Conventional solar cell manufacturing processes are highly labor intensive and have numerous interruptions that can affect production line throughput, solar cell cost, and device yield. Typical solar cell qualification and testing devices utilize lamps that are configured to expose a substrate to a beam of light, and probes to detect the current generated. The lamps are positioned above the substrate and configured to shine a beam of light downwardly toward the horizontally positioned substrate. Additionally, a voltage is delivered to an edge region of the substrate to test the breakthrough voltage by manually attaching an electrical lead from a power supply to the edge region of the substrate. As the demand for using increasingly larger substrates and higher production throughput continues to grow, the floor space, time, and labor required for such testing and qualification hardware in fabrication facilities becomes problematic due to maintenance, cost of ownership, and throughput issues.
Therefore, there is a need for an automated test apparatus for photovoltaic substrates that provides for automated testing in a compact, easily maintained unit for use in high-volume manufacturing facilities.